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For
use with Chapter 8
Universal Gravitation
Earth
on a Diet?
Posted May 15, 2000
New
evidence has come to light that Earth has lost weight - or,
to be more accurate, it has "lost" mass. However, Earth didn't
actually lose any mass. Using new measurement techniques,
scientists have determined that the mass of our planet is
actually less than originally thought.
On
Saturday, April 29, 2000, at a meeting of the American Physical
Society, the revised mass was announced. Previously, it was
calculated that Earth had a mass of 5.978 x 10e21
metric tons. Now, by using a more precise method of measuring,
scientists have determined that Earth has a mass of 5.972
x 10e21 metric tons. While this is only a difference
of about one-tenth of one percent, it means that the calculation
was off by about 6 sextillion metric tons.
This
recalculation was sparked by a recalculation of the gravitational
constant G. A physicist at the University of Washington did
this by making improvements to Cavendish’s experiment that
was used to calculate G in the 18th century.
If
this new value is universally accepted by the scientific community,
it would have an impact on the accuracy of current calculations
of the magnitude of the force of gravity. Still, the data
is preliminary and subject to change upon further experimentation.
It will help reduce the uncertainty by a factor of 100. But
before this value is accepted by the International Committee
for Data for Science and Technology, the research must be
reviewed and duplicated.
Activity
Use
the Internet sites given here to learn how the gravitational
constant is determined. Write an article in your Science Journal
explaining why it is inaccurate to say that the weight of
the Earth has changed.
References
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